This invention relates to master alloys and, more particularly to a master alloy for modifying the aluminum-silicon eutectic component of aluminum-silicon eutectic and hypo-eutectic casting alloys.
Strontium, either per se or in the form of a strontium-aluminum master alloy, is known to be a superior and permanent modifier of the aluminum-silicon eutectic in eutectic and hypoeutectic (less than 12.6 weight percent of silicon) aluminum-silicon casting alloys. Modification of the aluminum-silicon eutectic results in enhanced properties of the alloys, such as increased tensile strength. Thus, according to U.S. Pat. No. 3,466,170, U.S. Pat. No. 3,567,429, Canadian Patent No. 829,816 and K. Alker et al., "Experiences with the Permanent Modification of Al-Si Casting Alloys," published in Aluminum, 48(5), 362-367 (1972), the use of alkaline earth metals (e.g., strontium) as modifiers for aluminum-silicon alloys improves the casting properties of the latter, especially when these alloys are at or near the eutectic composition, which is the composition at which the melting point of the alloy is at a minimum. However, the manufacture of such a master alloy, containing, for example, about 10 weight percent strontium and 90 percent aluminum, is subject to the disadvantage that the strontium metal added to molten aluminum to form the master alloy is not only expensive but also oxidizes when exposed to air and burns upon fusion in contact with molten aluminum in the ambient atmosphere. A need has therefore existed in the aluminum casting field for a strontium-containing master alloy which is free of the aforesaid drawbacks.
Accordingly, it is an object of the present invention to provide an improved stontium-containing master alloy for modifying the structure of eutectic and hypo-eutectic aluminum-silicon casting alloys.
Another object is to provide a process for producing an improved strontium-containing master alloy for modifying the structure of eutectic and hypo-eutectic aluminum-silicon casting alloys.
These and other objects of the present invention as well as a fuller understanding of the advantages thereof can be had by reference to the following detailed description and claims.